Objectives: Systemic lupus erythematosus (SLE), a chronic illness with an unpredictable and variable course, profoundly affects the quality of life (QOL). General health questionnaires are used to assess QOL in SLE, but a disease-specific instrument could offer enhanced responsiveness and content validity. We detail the steps we took to develop and validate a new SLE-specific QOL instrument, SLEQOL.
Methods: Rheumatology professionals nominated items that they felt were important determinants of QOL of SLE patients. One hundred SLE patients were asked to assess the importance and frequency of occurrence of these items and to suggest those that had not been listed. Item reduction was performed using Rasch model and factor analyses to create a new questionnaire in English. This final questionnaire was administered to a cohort of 275 patients to study its psychometric properties.
Results: Fifty-one items covering a wide range of QOL concerns were identified. The patients' responses led to the elimination of 11. The new questionnaire of 40 items was found to have Cronbach's alpha of 0.95 and to consist of eight domains covering physical, mental and social QOL issues. It has good test-retest reliability, poor to fair cross-sectional correlation with the SF-36, with poor correlation with lupus activity or damage indices. The SLEQOL was more responsive to change than the SF-36.
Conclusions: We have developed a new 40-item SLEQOL in English and showed that it is valid for use in SLE patients in Singapore. It offers better content validity and responsiveness to change than the SF-36.